1. Field of the Invention
The invention which relates to an automatic drain device for pneumatic circuits concerns more particularly a membrane device advantageously replacing valve systems and finds a preferred application in circuits supplying automatic medical analysis apparatus with compressed air.
Compressed air circuits which feed apparatus comprising for examle pneumatic valves usually include filters for blocking the impurities which might disturb the operation and sealing of the valves. Each feed circuit is also provided with a jar in which the air penetrates before passing thorough the filter and reaching the valves, which jar makes possible condensation of the water vapor with which the compressed air is laden. It is in fact desirable to eliminate this water vapor which is a source of oxidation of the mechanical parts met with. The condensed water is collected by the jar and must be removed either continuously or episodically.
2. Description of the Prior Art
Manual drain devices are known which consist of a simple closure valve placed at the base of the jar and operated by a push button against the return force of a spring. It is of course necessary to operate them whenever required and that imposes on the user frequent supervision which is then a constraint, this is why this manual solution is very often replaced by an automatic drain device. There exists a system which consists in providing in this jar a small calibrate and constant leak aperture, through which the water escapes continually. But the aperture also creates an air leak which may seem negligible for high compressed air pressures but which is inadmissible in the case of lower pressures. It is then preferable to use a valve device urged to an open position by a spring and which is closed when the air pressure is established in the jar. As soon as the compressed air feed is interrupted, the valve opens again and the water may flow out of the jar. This arrangement uses essentially metal mechanical parts which may also oxidize and become rapidly defective. Furthermore, although the valve closes correctly at high pressures it is much more haphazard for low pressures.
An automatic drain device is further known which uses a valve mounted on a rod sliding in the jar and separating two chambers, a lower chamber communicating with the outside and an upper chamber recovering the condensed water and releases it to the lower chamber when a certain pressure is established above the valve. This system is not wholly satisfactory either, for it is difficult to use and to adjust.